vendor github.com/containers/image/v5@v5.5.1

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

1 files changed, 704 insertions, 72 deletions

diff --git a/vendor/github.com/klauspost/compress/huff0/decompress.go b/vendor/github.com/klauspost/compress/huff0/decompress.go
index fb42a398b..a03b2634a 100644
--- a/vendor/github.com/klauspost/compress/huff0/decompress.go
+++ b/vendor/github.com/klauspost/compress/huff0/decompress.go
@@ -25,6 +25,9 @@ type dEntryDouble struct {
 	len   uint8
 }
 
+// Uses special code for all tables that are < 8 bits.
+const use8BitTables = true
+
 // ReadTable will read a table from the input.
 // The size of the input may be larger than the table definition.
 // Any content remaining after the table definition will be returned.
@@ -83,6 +86,7 @@ func ReadTable(in []byte, s *Scratch) (s2 *Scratch, remain []byte, err error) {
 		}
 		v2 := v & 15
 		rankStats[v2]++
+		// (1 << (v2-1)) is slower since the compiler cannot prove that v2 isn't 0.
 		weightTotal += (1 << v2) >> 1
 	}
 	if weightTotal == 0 {
@@ -142,12 +146,14 @@ func ReadTable(in []byte, s *Scratch) (s2 *Scratch, remain []byte, err error) {
 		d := dEntrySingle{
 			entry: uint16(s.actualTableLog+1-w) | (uint16(n) << 8),
 		}
-		single := s.dt.single[rankStats[w] : rankStats[w]+length]
+		rank := &rankStats[w]
+		single := s.dt.single[*rank : *rank+length]
 		for i := range single {
 			single[i] = d
 		}
-		rankStats[w] += length
+		*rank += length
 	}
+
 	return s, in, nil
 }
 
@@ -208,7 +214,10 @@ func (d *Decoder) Decompress1X(dst, src []byte) ([]byte, error) {
 	if len(d.dt.single) == 0 {
 		return nil, errors.New("no table loaded")
 	}
-	var br bitReader
+	if use8BitTables && d.actualTableLog <= 8 {
+		return d.decompress1X8Bit(dst, src)
+	}
+	var br bitReaderShifted
 	err := br.init(src)
 	if err != nil {
 		return dst, err
@@ -216,17 +225,6 @@ func (d *Decoder) Decompress1X(dst, src []byte) ([]byte, error) {
 	maxDecodedSize := cap(dst)
 	dst = dst[:0]
 
-	decode := func() byte {
-		val := br.peekBitsFast(d.actualTableLog) /* note : actualTableLog >= 1 */
-		v := d.dt.single[val]
-		br.bitsRead += uint8(v.entry)
-		return uint8(v.entry >> 8)
-	}
-	hasDec := func(v dEntrySingle) byte {
-		br.bitsRead += uint8(v.entry)
-		return uint8(v.entry >> 8)
-	}
-
 	// Avoid bounds check by always having full sized table.
 	const tlSize = 1 << tableLogMax
 	const tlMask = tlSize - 1
@@ -238,11 +236,25 @@ func (d *Decoder) Decompress1X(dst, src []byte) ([]byte, error) {
 
 	for br.off >= 8 {
 		br.fillFast()
-		buf[off+0] = hasDec(dt[br.peekBitsFast(d.actualTableLog)&tlMask])
-		buf[off+1] = hasDec(dt[br.peekBitsFast(d.actualTableLog)&tlMask])
+		v := dt[br.peekBitsFast(d.actualTableLog)&tlMask]
+		br.advance(uint8(v.entry))
+		buf[off+0] = uint8(v.entry >> 8)
+
+		v = dt[br.peekBitsFast(d.actualTableLog)&tlMask]
+		br.advance(uint8(v.entry))
+		buf[off+1] = uint8(v.entry >> 8)
+
+		// Refill
 		br.fillFast()
-		buf[off+2] = hasDec(dt[br.peekBitsFast(d.actualTableLog)&tlMask])
-		buf[off+3] = hasDec(dt[br.peekBitsFast(d.actualTableLog)&tlMask])
+
+		v = dt[br.peekBitsFast(d.actualTableLog)&tlMask]
+		br.advance(uint8(v.entry))
+		buf[off+2] = uint8(v.entry >> 8)
+
+		v = dt[br.peekBitsFast(d.actualTableLog)&tlMask]
+		br.advance(uint8(v.entry))
+		buf[off+3] = uint8(v.entry >> 8)
+
 		off += 4
 		if off == 0 {
 			if len(dst)+256 > maxDecodedSize {
@@ -259,13 +271,196 @@ func (d *Decoder) Decompress1X(dst, src []byte) ([]byte, error) {
 	}
 	dst = append(dst, buf[:off]...)
 
-	for !br.finished() {
+	// br < 8, so uint8 is fine
+	bitsLeft := uint8(br.off)*8 + 64 - br.bitsRead
+	for bitsLeft > 0 {
 		br.fill()
+		if false && br.bitsRead >= 32 {
+			if br.off >= 4 {
+				v := br.in[br.off-4:]
+				v = v[:4]
+				low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+				br.value = (br.value << 32) | uint64(low)
+				br.bitsRead -= 32
+				br.off -= 4
+			} else {
+				for br.off > 0 {
+					br.value = (br.value << 8) | uint64(br.in[br.off-1])
+					br.bitsRead -= 8
+					br.off--
+				}
+			}
+		}
 		if len(dst) >= maxDecodedSize {
 			br.close()
 			return nil, ErrMaxDecodedSizeExceeded
 		}
-		dst = append(dst, decode())
+		v := d.dt.single[br.peekBitsFast(d.actualTableLog)&tlMask]
+		nBits := uint8(v.entry)
+		br.advance(nBits)
+		bitsLeft -= nBits
+		dst = append(dst, uint8(v.entry>>8))
+	}
+	return dst, br.close()
+}
+
+// decompress1X8Bit will decompress a 1X encoded stream with tablelog <= 8.
+// The cap of the output buffer will be the maximum decompressed size.
+// The length of the supplied input must match the end of a block exactly.
+func (d *Decoder) decompress1X8Bit(dst, src []byte) ([]byte, error) {
+	if d.actualTableLog == 8 {
+		return d.decompress1X8BitExactly(dst, src)
+	}
+	var br bitReaderBytes
+	err := br.init(src)
+	if err != nil {
+		return dst, err
+	}
+	maxDecodedSize := cap(dst)
+	dst = dst[:0]
+
+	// Avoid bounds check by always having full sized table.
+	dt := d.dt.single[:256]
+
+	// Use temp table to avoid bound checks/append penalty.
+	var buf [256]byte
+	var off uint8
+
+	shift := (8 - d.actualTableLog) & 7
+
+	//fmt.Printf("mask: %b, tl:%d\n", mask, d.actualTableLog)
+	for br.off >= 4 {
+		br.fillFast()
+		v := dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+0] = uint8(v.entry >> 8)
+
+		v = dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+1] = uint8(v.entry >> 8)
+
+		v = dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+2] = uint8(v.entry >> 8)
+
+		v = dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+3] = uint8(v.entry >> 8)
+
+		off += 4
+		if off == 0 {
+			if len(dst)+256 > maxDecodedSize {
+				br.close()
+				return nil, ErrMaxDecodedSizeExceeded
+			}
+			dst = append(dst, buf[:]...)
+		}
+	}
+
+	if len(dst)+int(off) > maxDecodedSize {
+		br.close()
+		return nil, ErrMaxDecodedSizeExceeded
+	}
+	dst = append(dst, buf[:off]...)
+
+	// br < 4, so uint8 is fine
+	bitsLeft := int8(uint8(br.off)*8 + (64 - br.bitsRead))
+	for bitsLeft > 0 {
+		if br.bitsRead >= 64-8 {
+			for br.off > 0 {
+				br.value |= uint64(br.in[br.off-1]) << (br.bitsRead - 8)
+				br.bitsRead -= 8
+				br.off--
+			}
+		}
+		if len(dst) >= maxDecodedSize {
+			br.close()
+			return nil, ErrMaxDecodedSizeExceeded
+		}
+		v := dt[br.peekByteFast()>>shift]
+		nBits := uint8(v.entry)
+		br.advance(nBits)
+		bitsLeft -= int8(nBits)
+		dst = append(dst, uint8(v.entry>>8))
+	}
+	return dst, br.close()
+}
+
+// decompress1X8Bit will decompress a 1X encoded stream with tablelog <= 8.
+// The cap of the output buffer will be the maximum decompressed size.
+// The length of the supplied input must match the end of a block exactly.
+func (d *Decoder) decompress1X8BitExactly(dst, src []byte) ([]byte, error) {
+	var br bitReaderBytes
+	err := br.init(src)
+	if err != nil {
+		return dst, err
+	}
+	maxDecodedSize := cap(dst)
+	dst = dst[:0]
+
+	// Avoid bounds check by always having full sized table.
+	dt := d.dt.single[:256]
+
+	// Use temp table to avoid bound checks/append penalty.
+	var buf [256]byte
+	var off uint8
+
+	const shift = 0
+
+	//fmt.Printf("mask: %b, tl:%d\n", mask, d.actualTableLog)
+	for br.off >= 4 {
+		br.fillFast()
+		v := dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+0] = uint8(v.entry >> 8)
+
+		v = dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+1] = uint8(v.entry >> 8)
+
+		v = dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+2] = uint8(v.entry >> 8)
+
+		v = dt[br.peekByteFast()>>shift]
+		br.advance(uint8(v.entry))
+		buf[off+3] = uint8(v.entry >> 8)
+
+		off += 4
+		if off == 0 {
+			if len(dst)+256 > maxDecodedSize {
+				br.close()
+				return nil, ErrMaxDecodedSizeExceeded
+			}
+			dst = append(dst, buf[:]...)
+		}
+	}
+
+	if len(dst)+int(off) > maxDecodedSize {
+		br.close()
+		return nil, ErrMaxDecodedSizeExceeded
+	}
+	dst = append(dst, buf[:off]...)
+
+	// br < 4, so uint8 is fine
+	bitsLeft := int8(uint8(br.off)*8 + (64 - br.bitsRead))
+	for bitsLeft > 0 {
+		if br.bitsRead >= 64-8 {
+			for br.off > 0 {
+				br.value |= uint64(br.in[br.off-1]) << (br.bitsRead - 8)
+				br.bitsRead -= 8
+				br.off--
+			}
+		}
+		if len(dst) >= maxDecodedSize {
+			br.close()
+			return nil, ErrMaxDecodedSizeExceeded
+		}
+		v := dt[br.peekByteFast()>>shift]
+		nBits := uint8(v.entry)
+		br.advance(nBits)
+		bitsLeft -= int8(nBits)
+		dst = append(dst, uint8(v.entry>>8))
 	}
 	return dst, br.close()
 }
@@ -274,15 +469,18 @@ func (d *Decoder) Decompress1X(dst, src []byte) ([]byte, error) {
 // The length of the supplied input must match the end of a block exactly.
 // The *capacity* of the dst slice must match the destination size of
 // the uncompressed data exactly.
-func (s *Decoder) Decompress4X(dst, src []byte) ([]byte, error) {
-	if len(s.dt.single) == 0 {
+func (d *Decoder) Decompress4X(dst, src []byte) ([]byte, error) {
+	if len(d.dt.single) == 0 {
 		return nil, errors.New("no table loaded")
 	}
 	if len(src) < 6+(4*1) {
 		return nil, errors.New("input too small")
 	}
+	if use8BitTables && d.actualTableLog <= 8 {
+		return d.decompress4X8bit(dst, src)
+	}
 
-	var br [4]bitReader
+	var br [4]bitReaderShifted
 	start := 6
 	for i := 0; i < 3; i++ {
 		length := int(src[i*2]) | (int(src[i*2+1]) << 8)
@@ -308,14 +506,7 @@ func (s *Decoder) Decompress4X(dst, src []byte) ([]byte, error) {
 
 	const tlSize = 1 << tableLogMax
 	const tlMask = tlSize - 1
-	single := s.dt.single[:tlSize]
-
-	decode := func(br *bitReader) byte {
-		val := br.peekBitsFast(s.actualTableLog) /* note : actualTableLog >= 1 */
-		v := single[val&tlMask]
-		br.bitsRead += uint8(v.entry)
-		return uint8(v.entry >> 8)
-	}
+	single := d.dt.single[:tlSize]
 
 	// Use temp table to avoid bound checks/append penalty.
 	var buf [256]byte
@@ -324,69 +515,484 @@ func (s *Decoder) Decompress4X(dst, src []byte) ([]byte, error) {
 
 	// Decode 2 values from each decoder/loop.
 	const bufoff = 256 / 4
-bigloop:
 	for {
-		for i := range br {
-			br := &br[i]
-			if br.off < 4 {
-				break bigloop
-			}
-			br.fillFast()
+		if br[0].off < 4 || br[1].off < 4 || br[2].off < 4 || br[3].off < 4 {
+			break
 		}
 
 		{
 			const stream = 0
-			val := br[stream].peekBitsFast(s.actualTableLog)
+			const stream2 = 1
+			br[stream].fillFast()
+			br[stream2].fillFast()
+
+			val := br[stream].peekBitsFast(d.actualTableLog)
 			v := single[val&tlMask]
-			br[stream].bitsRead += uint8(v.entry)
+			br[stream].advance(uint8(v.entry))
+			buf[off+bufoff*stream] = uint8(v.entry >> 8)
 
-			val2 := br[stream].peekBitsFast(s.actualTableLog)
+			val2 := br[stream2].peekBitsFast(d.actualTableLog)
 			v2 := single[val2&tlMask]
-			buf[off+bufoff*stream+1] = uint8(v2.entry >> 8)
-			buf[off+bufoff*stream] = uint8(v.entry >> 8)
-			br[stream].bitsRead += uint8(v2.entry)
+			br[stream2].advance(uint8(v2.entry))
+			buf[off+bufoff*stream2] = uint8(v2.entry >> 8)
+
+			val = br[stream].peekBitsFast(d.actualTableLog)
+			v = single[val&tlMask]
+			br[stream].advance(uint8(v.entry))
+			buf[off+bufoff*stream+1] = uint8(v.entry >> 8)
+
+			val2 = br[stream2].peekBitsFast(d.actualTableLog)
+			v2 = single[val2&tlMask]
+			br[stream2].advance(uint8(v2.entry))
+			buf[off+bufoff*stream2+1] = uint8(v2.entry >> 8)
 		}
 
 		{
-			const stream = 1
-			val := br[stream].peekBitsFast(s.actualTableLog)
+			const stream = 2
+			const stream2 = 3
+			br[stream].fillFast()
+			br[stream2].fillFast()
+
+			val := br[stream].peekBitsFast(d.actualTableLog)
 			v := single[val&tlMask]
-			br[stream].bitsRead += uint8(v.entry)
+			br[stream].advance(uint8(v.entry))
+			buf[off+bufoff*stream] = uint8(v.entry >> 8)
 
-			val2 := br[stream].peekBitsFast(s.actualTableLog)
+			val2 := br[stream2].peekBitsFast(d.actualTableLog)
 			v2 := single[val2&tlMask]
-			buf[off+bufoff*stream+1] = uint8(v2.entry >> 8)
-			buf[off+bufoff*stream] = uint8(v.entry >> 8)
-			br[stream].bitsRead += uint8(v2.entry)
+			br[stream2].advance(uint8(v2.entry))
+			buf[off+bufoff*stream2] = uint8(v2.entry >> 8)
+
+			val = br[stream].peekBitsFast(d.actualTableLog)
+			v = single[val&tlMask]
+			br[stream].advance(uint8(v.entry))
+			buf[off+bufoff*stream+1] = uint8(v.entry >> 8)
+
+			val2 = br[stream2].peekBitsFast(d.actualTableLog)
+			v2 = single[val2&tlMask]
+			br[stream2].advance(uint8(v2.entry))
+			buf[off+bufoff*stream2+1] = uint8(v2.entry >> 8)
+		}
+
+		off += 2
+
+		if off == bufoff {
+			if bufoff > dstEvery {
+				return nil, errors.New("corruption detected: stream overrun 1")
+			}
+			copy(out, buf[:bufoff])
+			copy(out[dstEvery:], buf[bufoff:bufoff*2])
+			copy(out[dstEvery*2:], buf[bufoff*2:bufoff*3])
+			copy(out[dstEvery*3:], buf[bufoff*3:bufoff*4])
+			off = 0
+			out = out[bufoff:]
+			decoded += 256
+			// There must at least be 3 buffers left.
+			if len(out) < dstEvery*3 {
+				return nil, errors.New("corruption detected: stream overrun 2")
+			}
+		}
+	}
+	if off > 0 {
+		ioff := int(off)
+		if len(out) < dstEvery*3+ioff {
+			return nil, errors.New("corruption detected: stream overrun 3")
+		}
+		copy(out, buf[:off])
+		copy(out[dstEvery:dstEvery+ioff], buf[bufoff:bufoff*2])
+		copy(out[dstEvery*2:dstEvery*2+ioff], buf[bufoff*2:bufoff*3])
+		copy(out[dstEvery*3:dstEvery*3+ioff], buf[bufoff*3:bufoff*4])
+		decoded += int(off) * 4
+		out = out[off:]
+	}
+
+	// Decode remaining.
+	for i := range br {
+		offset := dstEvery * i
+		br := &br[i]
+		bitsLeft := br.off*8 + uint(64-br.bitsRead)
+		for bitsLeft > 0 {
+			br.fill()
+			if false && br.bitsRead >= 32 {
+				if br.off >= 4 {
+					v := br.in[br.off-4:]
+					v = v[:4]
+					low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+					br.value = (br.value << 32) | uint64(low)
+					br.bitsRead -= 32
+					br.off -= 4
+				} else {
+					for br.off > 0 {
+						br.value = (br.value << 8) | uint64(br.in[br.off-1])
+						br.bitsRead -= 8
+						br.off--
+					}
+				}
+			}
+			// end inline...
+			if offset >= len(out) {
+				return nil, errors.New("corruption detected: stream overrun 4")
+			}
+
+			// Read value and increment offset.
+			val := br.peekBitsFast(d.actualTableLog)
+			v := single[val&tlMask].entry
+			nBits := uint8(v)
+			br.advance(nBits)
+			bitsLeft -= uint(nBits)
+			out[offset] = uint8(v >> 8)
+			offset++
+		}
+		decoded += offset - dstEvery*i
+		err = br.close()
+		if err != nil {
+			return nil, err
+		}
+	}
+	if dstSize != decoded {
+		return nil, errors.New("corruption detected: short output block")
+	}
+	return dst, nil
+}
+
+// Decompress4X will decompress a 4X encoded stream.
+// The length of the supplied input must match the end of a block exactly.
+// The *capacity* of the dst slice must match the destination size of
+// the uncompressed data exactly.
+func (d *Decoder) decompress4X8bit(dst, src []byte) ([]byte, error) {
+	if d.actualTableLog == 8 {
+		return d.decompress4X8bitExactly(dst, src)
+	}
+
+	var br [4]bitReaderBytes
+	start := 6
+	for i := 0; i < 3; i++ {
+		length := int(src[i*2]) | (int(src[i*2+1]) << 8)
+		if start+length >= len(src) {
+			return nil, errors.New("truncated input (or invalid offset)")
+		}
+		err := br[i].init(src[start : start+length])
+		if err != nil {
+			return nil, err
+		}
+		start += length
+	}
+	err := br[3].init(src[start:])
+	if err != nil {
+		return nil, err
+	}
+
+	// destination, offset to match first output
+	dstSize := cap(dst)
+	dst = dst[:dstSize]
+	out := dst
+	dstEvery := (dstSize + 3) / 4
+
+	shift := (8 - d.actualTableLog) & 7
+
+	const tlSize = 1 << 8
+	const tlMask = tlSize - 1
+	single := d.dt.single[:tlSize]
+
+	// Use temp table to avoid bound checks/append penalty.
+	var buf [256]byte
+	var off uint8
+	var decoded int
+
+	// Decode 4 values from each decoder/loop.
+	const bufoff = 256 / 4
+	for {
+		if br[0].off < 4 || br[1].off < 4 || br[2].off < 4 || br[3].off < 4 {
+			break
+		}
+
+		{
+			// Interleave 2 decodes.
+			const stream = 0
+			const stream2 = 1
+			br[stream].fillFast()
+			br[stream2].fillFast()
+
+			v := single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 := single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+1] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+1] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+2] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+3] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+3] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
 		}
 
 		{
 			const stream = 2
-			val := br[stream].peekBitsFast(s.actualTableLog)
-			v := single[val&tlMask]
-			br[stream].bitsRead += uint8(v.entry)
+			const stream2 = 3
+			br[stream].fillFast()
+			br[stream2].fillFast()
 
-			val2 := br[stream].peekBitsFast(s.actualTableLog)
-			v2 := single[val2&tlMask]
-			buf[off+bufoff*stream+1] = uint8(v2.entry >> 8)
-			buf[off+bufoff*stream] = uint8(v.entry >> 8)
-			br[stream].bitsRead += uint8(v2.entry)
+			v := single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 := single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+1] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+1] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+2] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+3] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+3] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+		}
+
+		off += 4
+
+		if off == bufoff {
+			if bufoff > dstEvery {
+				return nil, errors.New("corruption detected: stream overrun 1")
+			}
+			copy(out, buf[:bufoff])
+			copy(out[dstEvery:], buf[bufoff:bufoff*2])
+			copy(out[dstEvery*2:], buf[bufoff*2:bufoff*3])
+			copy(out[dstEvery*3:], buf[bufoff*3:bufoff*4])
+			off = 0
+			out = out[bufoff:]
+			decoded += 256
+			// There must at least be 3 buffers left.
+			if len(out) < dstEvery*3 {
+				return nil, errors.New("corruption detected: stream overrun 2")
+			}
+		}
+	}
+	if off > 0 {
+		ioff := int(off)
+		if len(out) < dstEvery*3+ioff {
+			return nil, errors.New("corruption detected: stream overrun 3")
+		}
+		copy(out, buf[:off])
+		copy(out[dstEvery:dstEvery+ioff], buf[bufoff:bufoff*2])
+		copy(out[dstEvery*2:dstEvery*2+ioff], buf[bufoff*2:bufoff*3])
+		copy(out[dstEvery*3:dstEvery*3+ioff], buf[bufoff*3:bufoff*4])
+		decoded += int(off) * 4
+		out = out[off:]
+	}
+
+	// Decode remaining.
+	for i := range br {
+		offset := dstEvery * i
+		br := &br[i]
+		bitsLeft := int(br.off*8) + int(64-br.bitsRead)
+		for bitsLeft > 0 {
+			if br.finished() {
+				return nil, io.ErrUnexpectedEOF
+			}
+			if br.bitsRead >= 56 {
+				if br.off >= 4 {
+					v := br.in[br.off-4:]
+					v = v[:4]
+					low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+					br.value |= uint64(low) << (br.bitsRead - 32)
+					br.bitsRead -= 32
+					br.off -= 4
+				} else {
+					for br.off > 0 {
+						br.value |= uint64(br.in[br.off-1]) << (br.bitsRead - 8)
+						br.bitsRead -= 8
+						br.off--
+					}
+				}
+			}
+			// end inline...
+			if offset >= len(out) {
+				return nil, errors.New("corruption detected: stream overrun 4")
+			}
+
+			// Read value and increment offset.
+			v := single[br.peekByteFast()>>shift].entry
+			nBits := uint8(v)
+			br.advance(nBits)
+			bitsLeft -= int(nBits)
+			out[offset] = uint8(v >> 8)
+			offset++
+		}
+		decoded += offset - dstEvery*i
+		err = br.close()
+		if err != nil {
+			return nil, err
+		}
+	}
+	if dstSize != decoded {
+		return nil, errors.New("corruption detected: short output block")
+	}
+	return dst, nil
+}
+
+// Decompress4X will decompress a 4X encoded stream.
+// The length of the supplied input must match the end of a block exactly.
+// The *capacity* of the dst slice must match the destination size of
+// the uncompressed data exactly.
+func (d *Decoder) decompress4X8bitExactly(dst, src []byte) ([]byte, error) {
+	var br [4]bitReaderBytes
+	start := 6
+	for i := 0; i < 3; i++ {
+		length := int(src[i*2]) | (int(src[i*2+1]) << 8)
+		if start+length >= len(src) {
+			return nil, errors.New("truncated input (or invalid offset)")
+		}
+		err := br[i].init(src[start : start+length])
+		if err != nil {
+			return nil, err
+		}
+		start += length
+	}
+	err := br[3].init(src[start:])
+	if err != nil {
+		return nil, err
+	}
+
+	// destination, offset to match first output
+	dstSize := cap(dst)
+	dst = dst[:dstSize]
+	out := dst
+	dstEvery := (dstSize + 3) / 4
+
+	const shift = 0
+	const tlSize = 1 << 8
+	const tlMask = tlSize - 1
+	single := d.dt.single[:tlSize]
+
+	// Use temp table to avoid bound checks/append penalty.
+	var buf [256]byte
+	var off uint8
+	var decoded int
+
+	// Decode 4 values from each decoder/loop.
+	const bufoff = 256 / 4
+	for {
+		if br[0].off < 4 || br[1].off < 4 || br[2].off < 4 || br[3].off < 4 {
+			break
 		}
 
 		{
-			const stream = 3
-			val := br[stream].peekBitsFast(s.actualTableLog)
-			v := single[val&tlMask]
-			br[stream].bitsRead += uint8(v.entry)
+			// Interleave 2 decodes.
+			const stream = 0
+			const stream2 = 1
+			br[stream].fillFast()
+			br[stream2].fillFast()
 
-			val2 := br[stream].peekBitsFast(s.actualTableLog)
-			v2 := single[val2&tlMask]
-			buf[off+bufoff*stream+1] = uint8(v2.entry >> 8)
-			buf[off+bufoff*stream] = uint8(v.entry >> 8)
-			br[stream].bitsRead += uint8(v2.entry)
+			v := single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 := single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+1] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+1] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+2] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+3] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+3] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
 		}
 
-		off += 2
+		{
+			const stream = 2
+			const stream2 = 3
+			br[stream].fillFast()
+			br[stream2].fillFast()
+
+			v := single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 := single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+1] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+1] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+2] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+2] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+
+			v = single[br[stream].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream+3] = uint8(v >> 8)
+			br[stream].advance(uint8(v))
+
+			v2 = single[br[stream2].peekByteFast()>>shift].entry
+			buf[off+bufoff*stream2+3] = uint8(v2 >> 8)
+			br[stream2].advance(uint8(v2))
+		}
+
+		off += 4
 
 		if off == bufoff {
 			if bufoff > dstEvery {
@@ -422,12 +1028,38 @@ bigloop:
 	for i := range br {
 		offset := dstEvery * i
 		br := &br[i]
-		for !br.finished() {
-			br.fill()
+		bitsLeft := int(br.off*8) + int(64-br.bitsRead)
+		for bitsLeft > 0 {
+			if br.finished() {
+				return nil, io.ErrUnexpectedEOF
+			}
+			if br.bitsRead >= 56 {
+				if br.off >= 4 {
+					v := br.in[br.off-4:]
+					v = v[:4]
+					low := (uint32(v[0])) | (uint32(v[1]) << 8) | (uint32(v[2]) << 16) | (uint32(v[3]) << 24)
+					br.value |= uint64(low) << (br.bitsRead - 32)
+					br.bitsRead -= 32
+					br.off -= 4
+				} else {
+					for br.off > 0 {
+						br.value |= uint64(br.in[br.off-1]) << (br.bitsRead - 8)
+						br.bitsRead -= 8
+						br.off--
+					}
+				}
+			}
+			// end inline...
 			if offset >= len(out) {
 				return nil, errors.New("corruption detected: stream overrun 4")
 			}
-			out[offset] = decode(br)
+
+			// Read value and increment offset.
+			v := single[br.peekByteFast()>>shift].entry
+			nBits := uint8(v)
+			br.advance(nBits)
+			bitsLeft -= int(nBits)
+			out[offset] = uint8(v >> 8)
 			offset++
 		}
 		decoded += offset - dstEvery*i